Electromagnetic transducer head



July 13, 1954 M. CAMRAS ELECTROMAGNETIC TRANsDUcEP. HEAD 2 Sheets-Sheet l Filed DeC. 23, 1948 mmm f77 yg f7 f!" Mmm @mms July 13, 1954 M. cAMRAs 2,683,774 ELECTROMAGNETIC TRANSDUC'ER HEAD Filed nec. 23, 194e 2 Sheets-Sheet 2 HVE'NZDP Marvin czmwczs Patented July 13, 1954 ELECTRQMAGNETIC TRANSDUCER- HEAD Marvin Camaras, Chicago, lll., assigner to Armour Research Foundation of Iilinois institute of Technoiegy, Illinois Chicago,

Ill., a corporation of Application Liecember 23, 1948, Serial No. 67,020

(Ci. ira- 1902) il Ciaims. 1

This .invention relates to magnetic recording apparatus, and more particularly, to electromagnetic transducer heads adaptable to both single and double track magnetic record tapes.

One of the greatest sources or". difficulty in the manufacture of magnetic recording and reproducing apparatus has always been the manufacture and design of the electromagnetic transducer head employed thereon. The particular nature and characteristics of the magnetic oircuits of the head have been found to be extrernely important in the fidelity oi response and eiiiciency of operation. The extremely small dimensions have also presented problems or" manufacture which have heretofore kept the cost of heads unduly high.

One of the principal features and objects of the present invention is to provide a novel elec-- tromagnetic transducer head which is economical to manufacture, which is eicient in operation, which gives high fidelity response and which readily lends itself to close control or tolerances in its manufacture,

A further object of the present invention is to provide a new and improved core structure for an electromagnetic transducer head.

Still another object of the present invention is to provide a novel and improved electromagnetic transducer head assembly.

Another and still further object oi the present invention is to provide a novel housing and mounting structure for a recording and reproducing head and ior an erase head.

further object or the present invention is to provide a novel means for minimizing the physical wear of the active magnetic portions of magr ic heads in electromagnetic transducer assemblies.

Another and still further object o the present invention is to provide a novel casing means for an electromagnetic transducer assembly which will greatly simplify the alignment and assembly of magnetic heads mounted therein.

The novel features which believe to be characteristic oi my invention are set forth with particular-it the appended claims. My invention itself, however, both as to its manner of construction and method of operation, together with other objects and advantages thereoi may best be understood. by reference to the following description taken in connection with the accompanying drawings, in which:

Figure l is a perspective View or" a magnetic head embodying my invention;

Figure 2 is a sectional view of the structure shown in Figure 1 as taken on line II--II;

Figure 3 is another sectional View of the magnetic head shown in Figure 1 as taken on line IlI-II of Figure 2;

Figure 4 is still another sectional View of the 2 magnetic head shown in Figure l as taken on line V-IEV of Figure 2;

Figure 5 is a view of some of the parts as taken on line V-V of Figure 3;

Figure 6 is an unassenibled View of some of the utilized in my invention;

Figure 7 is a perspective View of another structural embodiment or" my invention;

Efigure S is a sectional view of the magnetic head shown in Figure 7 as taken on line VIII-VIH;

Figure 9 `is another sectional View of the embodiment shown in Figure 7; and

Figure lo is a fragmentary sectional view of sti another embodiment oi the present inve tion.

Referring now more particularly to the drawings, Figure l shows a magnetic head assembly il for a tape recorder, indicating the manner in which two electromagnetic transducer heads comprising a record-playback head il and an erase head l2 are aligned horizontally in a slightly protrude-:i position above the sides of their hou g to allow easy engagement with the record members passing over their faces. A pair of magnetic keepers i3 made of high-permeability low-retentivity magnetic material are formed in the shape of cylindrical spacers having the same radius of curvature as the tops of the heads il and l2, and are also disposed within the assembly housing alongside each other, one on each oi the axes on which the heads Il and i2 are disposed. Each of the keepers i3 is separated from its corresponding adjacently disposed head by a relatively thin spacer washer I4 made of non-magnetic material such as brass.

The housing for the assembly It is made of non-nagnetic material., such as a suitable plastic composition, and consists oi two parts, namely; a base plate I5 to which the keepers i3 are secured and a protective cap it enclosing the energizing coils and magnetic circuits for the leads Ii and l2. The sides of the cap It are slightly recessed and curved at the top to provide a guide path ybetween the top portions oi base plate i5 and the cap it for record members as they pass over the heads and keepers Il, I2 and I.

The outward appearance of the active heads l l and l2 and the keepers i3 when assembled are similar except that the heads are each provided 1 ith a close tolerance air gap across the tip, the gap in the recording head being somewhat smaller than the erase head gap. The heads themselves, therefore, are substantially identical in appearance, but their magnetic circuit elements within the housing are somewhat different.

The magnetic circuits or" the transducer heads il and l2 consist of a pair of pole tip members i8 and 1S, respectively, and magnetic yokes 20 and 2 I, respectively. Each pair of pole tip niembers is secured to a circular spacer-like support element .'22 which may be made of non-magnetic material such as brass or Bakelite and is xed thereto by suitable means such as by soldering or cementing at points 23. The tips of members i8 and i9 are curved about the outer periphery of the spacer-like support elements 22 and confront each other at the top of the assembly to form a rigid air gap for each of the heads. The tips of pole tip members i8 and i9 are beveled on their undersides to reduce the cross-sectional area of the tips and consequently increase the iiux density in the air gaps. A slit may be cut in the nonemagnetic spacer-like support just below the air gap to receive and position a gap spacer if desired. The pole tips of the members it and is may then be secured to the gap spacer by such means as solder or brazing material.

An energizing coil spool is slipped over one eX- tcnsion of each pair of pole tip members 22, and the yokes 2@ and 2l, respectively, are each slidably tted in their respective positions with one leg inserted into one of such coil spools. The magnetic circuits for the heads are preferably made of high-permeability lov/retentivty magnetic material and are made thin to reduce the amount of eddy current loss therein. The disassembled recording head il is illustrated in Figure 6. To assemble the parts as shown in Figure 2, the yoke is inserted between the extending pole tip legs it. The relative dimensions of the yoke are such that a frictional engaging relationship is formed between the pole tip eX- tensions and the yoke legs to hold the energizing coils and the magnetic circuits in proper assembled relationship. The erase head i2 is similarly held in assembled relationship by yoke 2i. Under certain conditions, however, an air space may be desirable between the pole tip extensions and the legs or the yoke members in.

Y order to reduce residual magnetism, and to aid in balancing.

The recording head li is provided with two energizing coils, one a relatively high frequency coil 2li and the other a somewhat larger audio frequency coil E, both of which are wound on similar portions of a common spool 26. The recording' head ii is thus arranged for magnetic recording in accordance with the principles explained in detail in the Marvin Camras United States Patent No. 2,351,004, issued on June 13, 1944i, in which recording is accomplished by superimposing a magnetic field varying in accordance with an audio frequency signal upon a relatively high frequency eld. rlhe recording head i l is also used as a playback head, but during such operation, the high frequency eld windings are not energized and only the audio currents induced in the audio coil are amplified for reproduction.

The erase head i2 is provided with only one energizing coil 2S which is vwound on the spool 29. During operation, erase coil 28 is fed by the same high frequency oscillator. As a matter oi' fact, the erase coil can be connected in series with the high frequency recording coil, if desired, since the erase operation during magnetic recording Ais normally performed at the same time that a recording is being made.

To make the assembly lil more compact, each vof the coil spools 2t and 29 is provided with a d and 3i, beside enabling compactness, also provide means for properly positioning the heads i l and i2 and maintaining physical separation of the magnetic circuits.

fi pair of special mounting studs 32 hold the parts of the magnetic assembly i@ together. itach or the studs is provided with an unthreaded shank portion, on which one of the magnetic heads, a spacer i4, and a keeper i3 are mounted and secured by a hex nut 33 tightened onto a threaded end portion of the studs 32. The housing cap M5 is also held in its assembled position by the studs 32 by providing two holes in the cap i6 into which the threaded end portions of the studs 32 may extend and then threading internally threaded, slotted cap nuts 3d, each inserted in a countersunk outer portion of the holes onto the threaded stud ends until the cap i3 is tightly secured to the base plate i5. rihe hex nut 33 on the inner surface of the cap l5 is provided with room by countersinking the inner surface edges of the holes within which the ends of the studs 32 extend.

Another embodiment of my invention is shown in Figure 7 which illustrates a magnetic head assembly 3S having a recording head 3d and an erase head its horizontally aligned and protruding from a magnetic record member path between a housing base plate il and a housing cap The appearance of magnetic head assembly Sii is somewhat similar to that shown in Figure l, except that two pairs of prongs are secured in the base plate lli and project therefrom to provide means whereby the whole unit may be plugged into a socket in equipment with which it be associated.

in Figures 8 and 9, the internal elements of the unit are illustrated. Energizing coils are provided on both legs of each magnetic structure for the magnetic heads in this embodiment, while in the case of erase head llo, a double yoke is provided in the magnetic circuit, thereby reducing the possibility of saturation that might otherwise occur in the yoke portion of the magnetic circuit to produce undesirable magnetic characteristics. t is apparent that such a double yoke magnetic circuit is not necessarily limited to erase heads but may in some instances also be desirable in the construction of recording heads.

The magnetic circuit for the recorA lng head il@ comprises pole tip members cui ed about and seclned to a non-magnetic spacerdike support member it and a U-shaped yoke fi having each of its legs extending up throi u-, a coil spool d8 to engage the inner surfaces of the extensions o pole tip members dfi. or" the spools is provided with two winding portions, one for the audio frequency coil de and .he smaller portion for a high frequency coil I winding the respective pairs of coils, they are wound in additive magnetic relationship. The two audio coils thus wound are connected in series, and their two remaining ends are each ccnnected to one of the prongs T e magnetic circuit for the magnetic erase head fit comprises a pair of pole tip members 5l curved about and secured to a non-magnetic spacer-like support d, while a pair c" yokes 53 and 5t each have their legs fitted within a hole of one of the pair of coil spools and extend upwardly to make irictional engagement with the extensions of pole tip members to provide a relationship which acts to maintain assembly of the magnetic circuit. Frictional engagement Ik .in

of the inner' yoke 53 is made by the yoke legs engaging the inner surfaces of the extensions of pole tip members 5I, while frictional engagement of the outer yoke 54 is caused by its ends engaging the outer surfaces of the extensions of pole tip members 5|.

The spools 55 are somewhat oval in shape to reduce the need for a large dimension across the width of the magnetic head and pocket spaces 56 corresponding to each are provided in cap 42 to reduce the depth of the unit 3B. The coils 58 are Wound on spools 55 in additive magnetic relationship and are connected in series with each other as well as in series with the pair or high frequency coils 5t wound on recording head 39. The leads for energizing the two pairs of series connected high frequency coils 50 and 58 are connected to prongs 44.

The whole magnetic head assembly 38 is held together by a pair of mounting studs 59 passing through the base plate 4i, then through a keeper G of magnetic material, a separator washer 6| of non-magnetic material, the spacer-like support for the magnetic circuits for the magnetic heads with which the stud is associated and then extending part-way through the cap 42.

In the illustrated embodiment, the keepers $6 are held closer to the base platel and the magnetic heads on top of them in order to keep the energizing coils 3, Sii and 58 away from the mushroomed securing ends of prongs 43 and ld. This is also done since pocket space cannot be readily provided in base plate 4l because of the prong positions therein. The asser ibly of parts is fastened together on base plate 5| by means of a hex nut as in the embodiment of Figure l, and a countersunk portion on the inner surface of cap Al2 provides space for the nut. A pair of slotted cap nuts S2 pass through the cap 42 from its outside surface and threadedly engage the threaded. ends of studs 5t. Countersuni; portions on the outer surface of the cap 42 are provided for cap nuts 62 so that they will not protrude too great a distance from the surface of housing cap 42.

In utilising the apparatus as a means for making a record on a traveling magnetizable record member, high frequency electric energy is fed to the coil 2d simultaneously with a feeding of the audio signal to the coil 25. High frequency electric energy is also fed to the coil 28 of the erase head for the purpose of demagnetizing the channel or" the tape passing over the erase head I2 prior to the time when it reaches the recording head ll. On playback, it will, of course, be understood that the erase head i2 is rendered inoperative by de-energi'aing the erase head coil 28, and the high frequency bias winding 24 of the record-playback head Il is also de-energized.

Figure lo illustrates a magnetic head assembly somewhat similar to the above described einbodb ments, but including record member support ele ments which perform the additional function of minimizing the wearing away of the active portions or the magnetic heads over which magnetic record members pass during operation of such heads. A non-magnetic shoe member 6# made of suitable wear-resistant material is disposed between a pair of aligned magnetic heads 65 and 6B. The top of the shoe is arranged to have a slightly arced surface to correspond to the path of record members passing across and between the two heads while the shoe itself is rigidly secured to a base plate 61 by suitable means such as a bolt 63; In addition to the shoe 68, record support is also provided by two non-magnetic wear-resistant side extension members E9 and 'i0 embedded in the sides of the cap member 'il (shown in cross-section). These side extension members are so disposed and shaped that their top surfaces are also in a line corresponding to the path over which the record members associated with the head assembly will pass during operation. As shown in Figure l), a straight line drawn between adjacent tifearu'esistant :embers cuts through the magnetic heads to a level only slightly below their top surfaces. Thus, when the active portions of the magnetic heads weer away, to such straight line levels as donned by the wear-resistant members disposed in the record member path, the magnetic heads '-.vill still be in substantially uneiiected state with regard to the periorinance of their respective functions.

While I have shown particuiar embodiments oi my invention, it will, of course, be understood that I do not wish to be limited thereto, since many modioations may be made, I, therefore, contemplate by the appended claims to cover all such modiaetions that fall within the true spirit and scope of my invention.

I claim as my invention:

l. In an electromagnetic transducer head, an elongated loop formed of paramagnetic material, said loop having a gap at one end formed by con fronting ends or" said material, the loop at said gap being sha-peo. to engage a traveling magnetic impulse record member passed thereover, a nonn magnetic circuit support member disposed within said loop, said confronting ends of said loop being xedly secured to the outer surface of said circuit support member and having free ends extending from said support member and at least one energizing coil surrounding a, portion 0i one of the free ends whereby said transducer head may be energized.

In an electromagnetic transducer head, an elongated loop formed of thin strip oi' parainagnetic material, said loop having a relatively small gap at one end formed between confronting ends or said material, said loop being shaped at said gap to engage a traveling magnetic impulse record member passed thereover, a circular support member made ol non-magnetic metal essentially equal in width to the width or said said loop surrounding said member and hat its confronting ends 's'edly secured to the outer circumference of said member and having free ends extending from said support member, and at least one energizing coil surrounding a portion of one of the free ends whereby said magnetic circuit may be energized.

3. An electromagnetic transducer head comprising a non-magnetic circular circuit support, a pair of paramagnetic pole tip members, said members each having an end curved about a portion of said support, said curved pole tip members being secured in confronting relationship to each other on said support members while the other ends of said members are arranged to extend tangentially from diametrically opposite sides oi" said support member in paraliel relationship to each other, a U-shaped paramagnetic yoke member having parallel leg portions extending between said parallel ends or' said pole tip members to make frictional magnetic junctions therewith and at least one energizing coil surrounding a junction so formed.

4. An electromagnetic transducer head coinprising a nom-magnetic circuit support member, a pair of paramagnetic pole tip members, said pole tip members each having an end secured to a portion of said support, said secured ends being arranged in confronting relationship to each other to form a gap between them, each of said confronting ends having `a beveled under-edge, said support member having a slot substantially as wide as said gap extending across said support member immediately below said gap, said pole tip members having their other ends extending from opposite sides of said support member in parallel relationship to each other, a U-shaped paramagnetic yoke member having parallel leg portions extending between said parallel ends of said pole tip members to make magnetic junctions therewith and at least one energizing coil surrounding a junction so formed.

5. An electromagnetic transducer head comprising a non-magnetic circuit support member,

a pair of paramagnetic pole tip members, said pole tip members each having an end secured to a portion of said support, said secured ends being arranged in confronting relationship to each other forming a gap between them, said pole tip members having their other ends extending from opposite sides of said support member in parallel relationship to each other, a U-shaped magnetic yoke having leg ends extending between said parallel pole tip ends and making engagement with the inner sides thereof, a second U-shaped magnetic yoke having leg ends making engagement with the outer sides of said pole tip members and at least one energizing coil wound about said magnetic yoke members whereby said transducer head may be energized.

6. In combination, an electromagnetic transducer head and a short circuiting magnetic keeper, said transducer head including a pair of confronting high-permeability low-retentivity magnetic pole tip members arranged to form an air gap therebetween, a non-magnetic member to support said confronting pole tip members, a magnetic yoke extending between the end portions of said pole tip members and at least one energizing coil wound on said magnetic yoke member, said keeper being disposed coaxially with said non-magnetic member and in close proximity thereto.

7. In an electromagnetic transducer unit, a recording head having a pair of confronting magnetic pole tip members spaced by a non-magnetic gap therebetween, a non-magnetic support member secured to said pole tip members at the region of said gap, said pole tip members having end portions extending below said support member in parallel relationship, and a separate U-shaped magnetic yoke having leg members extending upwardly between said end portions, the arms of said yoke engaging said end portions in snug frictional engagement.

8. An electromagnetic transducer assembly including two confronting magnetic pole tip members defining a nonmagnetic gap therebetween, a non-magnetic support member secured to said pole tip members and spacing said pole tip members to provide said non-magnetic gap, said pole tip members having end portions extending below said support in parallel relationship, a U-shaped magnetic yoke having leg members extending upwardly between said end portions and engaging the inner surfaces of said end portions in snug frictional engagement, and a second U-shaped magnetic yoke having leg members extending upwardly and in snug frictional contact with the outer surface of said end portions.

9. An electromagnetic transducer head assembly comprising a housing assembly of non-magnetic material and substantially enclosing a pair of transducer devices, said transducer devices having an elongated loop formed of paramagnetic material, said loop having a gap at one end formed by confronting ends of said material, the loop at said gap being shaped to engage a traveling magnetic impulse record member passed thereover, a non-magnetic circuit support member disposed within said loop and carried by said housing, said confronting ends of said loop being xedly secured to the outer surface of said circuit support member and having free ends extending from said support member, and at least one energizing coil surrounding a portion of one or said free ends whereby the transducer head may be energized.

10. An electromagnetic transducer head assembly comprising a housing of non-magnetic material substantially enclosing a pair of transducer devices and-having a base plate and a cover member, each of said electromagnetic transducer devices having an elongated loop formed of paramagnetic material, said loop having a gap at one end formed by confronting ends of said material, the loop at said gap being shaped to engage a traveling magnetic impulse record member passed thereover, a non-magnetic circuit support member disposed within said loop and supported by said base plate and said cover of said housing, said confronting ends of said loop being xedly secured to the outer surface of said circuit support member and having free ends extending from said support member, and at least one energizing coil surrounding a portion of one of the free ends whereby said transducer head may be energized.

l1. In an electromagnetic transducer head assembly, in combination, a housing formed of nonmagnetic material and substantially enclosing a pair of electromagnetic transducer devices, each of said electromagnetic transducer devices having a short circuiting magnetic keeper, said devices furtner including a pair of confronting highpermeability low-retentivity magnetic pole tip members arranged to form an air gap therebetween, a non-magnetic member to support said confronting pole tips and aixed to said housing, a magnetic yoke extending between the end portions of said pole tip members and at least one energizing coil wound on said yoke member, said keeper being disposed co-axially with said nonmagnetic member and in close proximity thereto.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,886,816 Jensen Nov. 8, 1932 1,941,477 Jensen Jan. 25, 1934 2,029,212 Quam Sept. 6, 1935 2,290,680 Franz July 21, 1942 2,380,300 Gaston July 10, 1945 2,411,849 Camras Dec. 3, 1946 2,413,108 Latchford Dec. 24, 1946 2,456,767 Camras Dec. 21, 1948 2,493,742 Begun Jan, 10, 1950 2,513,653 Kornei July 4, 1950 2,523,576 Kornei Sept. 26, 1950 2,536,272 Friend Jan. 2, 1951 2,540,406 Ranger Feb, 6, 1951 2,547,737 Blaney Apr. 3, 1951 2,549,771 Camras Apr. 24, 1951 FOREIGN PATENTS Number Country Date France Mar, 8, 1948 

